Comparison of Composition Ranges of TP316 Stainless Steel By wilsonpipeline.com

The specification of stainless steel bar (to BS970 EN 10088-3 ) and stainless steel tube plate (to BS1449) before 1983 covered two type 316 grades: a ‘low’ carbon with 0.03% max (316S12) and a ‘standard’ carbon with 0.07% max 316S16. Both had a molybdenum content in the range of 2.25-3.0 %.

The 1983 and subsequent versions of the standard introduced new molybdenum content ranges of 2.0-2.5% and 2.5-3.0% for both the low and ‘standard’ carbon grades, thereby increasing the number of these grades from two to four:

316S11 low carbon, lower molybdenum range

316S13 low carbon, higher molybdenum range

316S31 standard carbon, lower molybdenum range

316S33 standard carbon, higher molybdenum range

The chromium range was maintained across all of the grades at 16.5-18.5%, but the nickel range was adjusted to ‘balance’ the structure of these austenitic stainless steel. Nickel is an ‘austenite stabiliser’ and so is used to balance the combined effects of carbon (also an austenite stabiliser) and molybdenum which has the opposite effect as a ‘ferrite stabiliser’.

The only equivalent for the old 316S12 is the 316S13, so that the minimum molybdenum of 2.25 is met. Similarly, the only equivalent for the old 316S16 is the 316S33. For atmospheric exposure service conditions, except in extreme marine environments, the substitution of either

316S11 for 316S12 or 316S31 for 316S16 

should give satisfactory corrosion resistance, depending on design and finishing techniques.

Pre 1983 specifications to BS970-1 and stainless steel tube plate (to BS1449)

	316S12		316S16
	% min	% max.	% min	% max
C		0.03		0.07
Si	0.20	1.00	0.20	1.00
Mn	0.50	2.00	0.50	2.00
Ni	11.0	14.0	10.0	13.0
Cr	16.5	18.5	16.5	18.5
Mo	2.25	3.0	2.25	3.0
S		0.030		0.030
P		0.045		0.045

Post 1983 specifications to BS970-1 and stainless steel tube plate (to BS1449)

	316S11		316S13		316S31		316S33
	% min	% max	% min	% max	% min	% max	% min	% max
C		0.030		0.030		0.07		0.07
Si		1.0		1.0		1.0		1.0
Mn		2.0		2.0		2.0		2.0
Ni	11.0	14.0	11.5	14.5	10.5	13.5	11.0	14.0
Cr	16.5	18.5	16.5	18.5	16.5	18.5	16.5	18.5
Mo	2.00	2.50	2.50	3.00	2.00	2.50	2.50	3.00
S		0.030		0.030		0.030		0.030
P		0.045		0.045		0.045		0.045

Specification to EN 10088-2 and stainless steel bar (to EN 10088-3 )

In 1995 BS EN 10088-2 replaced BS1449 and BS EN 10088-3 replaced BS 970-1. The four 316 sub-grades have numerical designations as follows:

Former BS designation	316S11	316S13	316S31	316S33
Current BS EN numbers	1.4404	1.4432	1.4401	1.4436

Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

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